scholarly journals An Analysis of Convectively Coupled Kelvin Waves in 20 WCRP CMIP3 Global Coupled Climate Models

2010 ◽  
Vol 23 (11) ◽  
pp. 3031-3056 ◽  
Author(s):  
Katherine H. Straub ◽  
Patrick T. Haertel ◽  
George N. Kiladis
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Three Dimensional ◽  
Kelvin Waves ◽  
Global Climate Models ◽  
Specific Humidity ◽  
Tropospheric Temperature ◽  
Wave Band ◽  
Kelvin Wave ◽  
Shallow Convection

Abstract Output from 20 coupled global climate models is analyzed to determine whether convectively coupled Kelvin waves exist in the models, and, if so, how their horizontal and vertical structures compare to observations. Model data are obtained from the World Climate Research Program’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. Ten of the 20 models contain spectral peaks in precipitation in the Kelvin wave band, and, of these 10, only 5 contain wave activity distributions and three-dimensional wave structures that resemble the observations. Thus, the majority (75%) of the global climate models surveyed do not accurately represent convectively coupled Kelvin waves, one of the primary sources of submonthly zonally propagating variability in the tropics. The primary feature common to the five successful models is the convective parameterization. Three of the five models use the Tiedtke–Nordeng convective scheme, while the other two utilize the Pan and Randall scheme. The 15 models with less success at generating Kelvin waves predominantly contain convective schemes that are based on the concept of convective adjustment, although it appears that those schemes can be improved by the addition of convective “trigger” functions. Three-dimensional Kelvin wave structures in the five successful models resemble observations to a large degree, with vertically tilted temperature, specific humidity, and zonal wind anomalies. However, no model completely captures the observed signal, with most of the models being deficient in lower-tropospheric temperature and humidity signals near the location of maximum precipitation. These results suggest the need for improvements in the representations of shallow convection and convective downdrafts in global models.

scholarly journals Understanding Intermodel Variability in Future Projections of a Sahelian Storm Proxy and Southern Saharan Warming

2021 ◽  
Vol 34 (2) ◽  
pp. 509-525
Author(s):  
David P. Rowell ◽  
Rory G. J. Fitzpatrick ◽  
Lawrence S. Jackson ◽  
Grace Redmond
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Vertical Wind Shear ◽  
Global Climate Models ◽  
Tropospheric Temperature ◽  
Storm Activity ◽  
Convective Systems ◽  
The North ◽  
Projected Changes

AbstractProjected changes in the intensity of severe rain events over the North African Sahel—falling from large mesoscale convective systems—cannot be directly assessed from global climate models due to their inadequate resolution and parameterization of convection. Instead, the large-scale atmospheric drivers of these storms must be analyzed. Here we study changes in meridional lower-tropospheric temperature gradient across the Sahel (ΔTGrad), which affect storm development via zonal vertical wind shear and Saharan air layer characteristics. Projected changes in ΔTGrad vary substantially among models, adversely affecting planning decisions that need to be resilient to adverse risks, such as increased flooding. This study seeks to understand the causes of these projection uncertainties and finds three key drivers. The first is intermodel variability in remote warming, which has strongest impact on the eastern Sahel, decaying toward the west. Second, and most important, a warming–advection–circulation feedback in a narrow band along the southern Sahara varies in strength between models. Third, variations in southern Saharan evaporative anomalies weakly affect ΔTGrad, although for an outlier model these are sufficiently substantive to reduce warming here to below that of the global mean. Together these uncertain mechanisms lead to uncertain southern Saharan/northern Sahelian warming, causing the bulk of large intermodel variations in ΔTGrad. In the southern Sahel, a local negative feedback limits the contribution to uncertainties in ΔTGrad. This new knowledge of ΔTGrad projection uncertainties provides understanding that can be used, in combination with further research, to constrain projections of severe Sahelian storm activity.

Multimodel Analysis of the Water Vapor Feedback in the Tropical Upper Troposphere

2006 ◽  
Vol 19 (20) ◽  
pp. 5455-5464 ◽  
Author(s):  
Ken Minschwaner ◽  
Andrew E. Dessler ◽  
Parnchai Sawaengphokhai
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Sea Surface ◽  
Specific Humidity ◽  
Upper Troposphere ◽  
The Mean ◽  
Tropical Upper Troposphere

Abstract Relationships between the mean humidity in the tropical upper troposphere and tropical sea surface temperatures in 17 coupled ocean–atmosphere global climate models were investigated. This analysis builds on a prior study of humidity and surface temperature measurements that suggested an overall positive climate feedback by water vapor in the tropical upper troposphere whereby the mean specific humidity increases with warmer sea surface temperature (SST). The model results for present-day simulations show a large range in mean humidity, mean air temperature, and mean SST, but they consistently show increases in upper-tropospheric specific humidity with warmer SST. The model average increase in water vapor at 250 mb with convective mean SST is 44 ppmv K−1, with a standard deviation of 14 ppmv K−1. Furthermore, the implied feedback in the models is not as strong as would be the case if relative humidity remained constant in the upper troposphere. The model mean decrease in relative humidity is −2.3% ± 1.0% K−1 at 250 mb, whereas observations indicate decreases of −4.8% ± 1.7% K−1 near 215 mb. These two values agree within the respective ranges of uncertainty, indicating that current global climate models are simulating the observed behavior of water vapor in the tropical upper troposphere with reasonable accuracy.

scholarly journals Sustainable City Planning: A Data-Driven Approach for Mitigating Urban Heat

2021 ◽  
Vol 6 ◽  
Author(s):  
Andrew MacLachlan ◽  
Eloise Biggs ◽  
Gareth Roberts ◽  
Bryan Boruff
Keyword(s):  
Urban Areas ◽  
City Planning ◽  
Climate Models ◽  
Global Climate ◽  
Three Dimensional ◽  
Global Climate Models ◽  
Data Driven ◽  
Climate Data ◽  
Data Driven Approach ◽  
Urban Heat

Urban areas are expected to triple by 2030 in order to accommodate 60% of the global population. Anthropogenic landscape modifications expand coverage of impervious surfaces inducing the urban heat island (UHI) effect, a critical twenty first century challenge associated with increased economic expenditure, energy consumption, and adverse health impacts. Yet, omission of UHI measures from global climate models and metropolitan planning methodologies precludes effective sustainable development governance. We present an approach that integrates Earth observation and climate data with three-dimensional urban models to determine optimal tree placement (per square meter) within proposed urban developments to enable more effective localized UHI mitigation. Such data-driven planning decisions will enhance the future sustainability of our cities to align with current global urban development agendas.

scholarly journals Impacts of Vertical Structure of Convection in Global Warming: The Role of Shallow Convection

2016 ◽  
Vol 29 (12) ◽  
pp. 4665-4684 ◽  
Author(s):  
Chao-An Chen ◽  
Jia-Yuh Yu ◽  
Chia Chou
Keyword(s):  
Global Warming ◽  
Climate Models ◽  
Global Climate ◽  
Deep Convection ◽  
Atmospheric Stability ◽  
Detailed Examination ◽  
Global Climate Models ◽  
Shallow Convection ◽  
Tropical Circulation ◽  
Heavy Structure

Abstract Global-warming-induced changes in regional tropical precipitation are usually associated with changes in the tropical circulation, which is a dynamic contribution. This study focuses on the mechanisms of the dynamic contribution that is related to the partition of shallow convection in tropical convection. To understand changes in tropical circulation and its associated mechanisms, 32 coupled global climate models from CMIP3 and CMIP5 were investigated. The study regions are convection zones with positive precipitation anomalies, where both enhanced and reduced ascending motions are found. Under global warming, an upward-shift structure of ascending motion is observed in the entire domain, implying a deepening of convection and a more stable atmosphere, which leads to a weakening of the tropical circulation. In a more detailed examination, areas with enhanced (weakened) ascending motion are associated with more (less) import of moist static energy by a climatologically bottom-heavy (top heavy) structure of vertical velocity, which is similar to a “rich get richer” mechanism. In a warmer climate, different climatological vertical profiles tend to induce different changes in atmospheric stability: the bottom-heavy (top heavy) structure brings a more (less) unstable condition and is favorable (unfavorable) to the strengthening of the convective circulation. The bottom-heavy structure is associated with shallow convection, while the top-heavy structure is usually related to deep convection. This study suggests a hypothesis and a possible linkage for projecting and understanding future circulation change from the current climate: shallow convection will tend to strengthen tropical circulation and enhance upward motion in a future warmer climate.

Diffusive Staircases in Shear: Dynamics and Heat Transport

2021 ◽  
Author(s):  
Justin M. Brown ◽  
Timour Radko
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Three Dimensional ◽  
Dynamic Environment ◽  
Global Climate Models ◽  
The Arctic ◽  
Boussinesq Fluid ◽  
Background Shear

AbstractArctic staircases mediate the heat transport from the warm water of Atlantic origin to the cooler waters of the Arctic mixed layer. For this reason, staircases have received much due attention from the community, and their heat transport has been well characterized for systems in the absence of external forcing. However, the ocean is a dynamic environment with large-scale currents and internal waves being omnipresent, even in regions shielded by sea-ice. Thus, we have attempted to address the effects of background shear on fully developed staircases using numerical simulations. The code, which is pseudo-spectral, evolves the governing equations for a Boussinesq fluid with temperature and salinity in a shearing coordinate system. We find that—– unlike many other double-diffusive systems—the sheared staircase requires three-dimensional simulations to properly capture the dynamics. Our simulations predict shear patterns that are consistent with observations and show that staircases in the presence of external shear should be expected to transport heat and salt at least twice as efficiently as in the corresponding non-sheared systems. These findings may lead to critical improvements in the representation of micro-scale mixing in global climate models.

scholarly journals Evaluating the effect of the statistical downscaling method on monthly precipitation estimates of global climate models

2021 ◽  
Keyword(s):  
Climate Models ◽  
Prediction Models ◽  
Global Climate ◽  
Linear Regression Analysis ◽  
Pressure Level ◽  
Global Climate Models ◽  
Specific Humidity ◽  
Monthly Precipitation ◽  
Estimation Errors ◽  
Downscaling Method

<p>Researches to foresee the possible effects of climate change on the environment and living beings for taking necessary precautions on time have increased in recent years. In the improvement of these studies, especially the reduction of estimation errors by downscaling the outputs of global climate models played an important role. In this study, a model that can predict monthly precipitation amounts in the future by using downscaling methods in different global climate models were applied in Antakya district of Hatay province, and the model results were evaluated. The predictive parameters for global climate models were determined using downscaling methods by applying correlation analysis for the study area. As a result of this analysis, it was seen that the air temperature and specific humidity values at the pressure level of 925 hPa and the geopotential height value at the 300 hPa pressure level had the best correlation for the years 1970-2005. The usability of three different global climate models (CanESM2, GISS-E2H, and CSIRO Mk 3-6-0) for the forecast of future rainfall in the Antakya district of Hatay province was investigated using multiple linear regression analysis, one of the downscaling methods. As a result of the statistical analysis, it was seen that the use of the downscaling method increased the accuracy of all prediction models.</p>

scholarly journals Driving a high-resolution dynamic ice-sheet model with GCM climate: ice-sheet initiation at 116 000 BP

1997 ◽  
Vol 25 ◽  
pp. 296-304 ◽  
Author(s):  
David Pollard ◽  
Starley L. Thompson
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Grid Point ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Horizontal Resolution ◽  
Global Climate Models ◽  
Surface Mass ◽  
Elevation Correction

AbstractMost dynamic ice-sheet studies currently use either empirically based parameterizations or simple energy-balance climate models for the surface mass-balance forcing. If three-dimensional global climate models (GCMs) could be used instead, they would greatly improve the potential realism of coupled climate ice-sheet simulations. However, there are two serious problems in simulating realistic mass balances on ice sheets from GCM simulations: (i) dynamic ice-sheet models and the underlying bedrock topography need horizontal resolution of 50–100 km or less, but the finest practical resolution of atmospheric GCMs is currently ˜250 km, and (ii) GCM surface physics usually neglects the local refreezing of meltwater on ice sheets.Two techniques are described that address these problems: an elevation correction applied to the atmospheric GCM fields interpolated to the ice-sheet grid, and a refreezing correction involving the annual totals of snowfall, rainfall and local melt at each grid-point. As an example of their use, we have used the GENESIS version 2 GCM at 3.75° × 3.75° resolution to simulate the climate at the end of the last interglaciation at ˜116 000 years ago. The atmospheric climate is then used to drive a standard two-dimensional dynamic ice-sheet model for 10 000 years on a 0.5° × 0.5° grid spanning northern North America. The model successfully predicts ice-sheet initiation over the Baffin Island highlands and the Canadian Archipelago, but at a slower rate than observed. A large ice sheet nucleates and grows rapidly over the northwestern Rockies, in conflict with geologic evidence. Possible reasons for these discrepancies are discussed.

scholarly journals Evaluating the Performance of Land Surface Models

2008 ◽  
Vol 21 (21) ◽  
pp. 5468-5481 ◽  
Author(s):  
Gab Abramowitz ◽  
Ray Leuning ◽  
Martyn Clark ◽  
Andy Pitman
Keyword(s):  
Statistical Models ◽  
Land Surface ◽  
Climate Models ◽  
Performance Metrics ◽  
Global Climate ◽  
Global Climate Models ◽  
Specific Humidity ◽  
Model Complexity ◽  
Land Surface Models ◽  
Surface Models

Abstract This paper presents a set of analytical tools to evaluate the performance of three land surface models (LSMs) that are used in global climate models (GCMs). Predictions of the fluxes of sensible heat, latent heat, and net CO2 exchange obtained using process-based LSMs are benchmarked against two statistical models that only use incoming solar radiation, air temperature, and specific humidity as inputs to predict the fluxes. Both are then compared to measured fluxes at several flux stations located on three continents. Parameter sets used for the LSMs include default values used in GCMs for the plant functional type and soil type surrounding each flux station, locally calibrated values, and ensemble sets encompassing combinations of parameters within their respective uncertainty ranges. Performance of the LSMs is found to be generally inferior to that of the statistical models across a wide variety of performance metrics, suggesting that the LSMs underutilize the meteorological information used in their inputs and that model complexity may be hindering accurate prediction. The authors show that model evaluation is purpose specific; good performance in one metric does not guarantee good performance in others. Self-organizing maps are used to divide meteorological “‘forcing space” into distinct regions as a mechanism to identify the conditions under which model bias is greatest. These new techniques will aid modelers to identify the areas of model structure responsible for poor performance.

Implementation and evaluation of a double-plume convective parameterization in NCAR CAM5

2021 ◽  
pp. 1-51
Author(s):  
Wenchao Chu ◽  
Yanluan Lin ◽  
Ming Zhao
Keyword(s):  
Climate Models ◽  
Marine Boundary Layer ◽  
Cloud Model ◽  
Global Climate ◽  
Global Climate Models ◽  
Shallow Convection ◽  
Unified Framework ◽  
Monsoon Period ◽  
Tropical Precipitation ◽  
Single Column

AbstractPerformance of global climate models (GCMs) is strongly affected by their cumulus parameterizations (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates and closures. The scheme was tested in single column, short-term hindcast and AMIP simulations. Compared with the default combination of Zhang-McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.

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